package com.trilead.ssh2;

import java.io.IOException;
import java.io.InputStream;

/**
 * A <code>StreamGobbler</code> is an InputStream that uses an internal worker
 * thread to constantly consume input from another InputStream. It uses a buffer
 * to store the consumed data. The buffer size is automatically adjusted, if
 * needed.
 * <p>
 * This class is sometimes very convenient - if you wrap a session's STDOUT and
 * STDERR InputStreams with instances of this class, then you don't have to
 * bother about the shared window of STDOUT and STDERR in the low level SSH-2
 * protocol, since all arriving data will be immediatelly consumed by the worker
 * threads. Also, as a side effect, the streams will be buffered (e.g., single
 * byte read() operations are faster).
 * <p>
 * Other SSH for Java libraries include this functionality by default in their
 * STDOUT and STDERR InputStream implementations, however, please be aware that
 * this approach has also a downside:
 * <p>
 * If you do not call the StreamGobbler's <code>read()</code> method often
 * enough and the peer is constantly sending huge amounts of data, then you will
 * sooner or later encounter a low memory situation due to the aggregated data
 * (well, it also depends on the Java heap size). Joe Average will like this
 * class anyway - a paranoid programmer would never use such an approach.
 * <p>
 * The term "StreamGobbler" was taken from an article called
 * "When Runtime.exec() won't", see
 * http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html.
 * 
 * @author Christian Plattner, plattner@trilead.com
 * @version $Id: StreamGobbler.java,v 1.1 2007/10/15 12:49:56 cplattne Exp $
 */

public class StreamGobbler extends InputStream {
	class GobblerThread extends Thread {
		@Override
		public void run() {
			byte[] buff = new byte[8192];

			while (true) {
				try {
					int avail = is.read(buff);

					synchronized (synchronizer) {
						if (avail <= 0) {
							isEOF = true;
							synchronizer.notifyAll();
							break;
						}

						int space_available = buffer.length - write_pos;

						if (space_available < avail) {
							/* compact/resize buffer */

							int unread_size = write_pos - read_pos;
							int need_space = unread_size + avail;

							byte[] new_buffer = buffer;

							if (need_space > buffer.length) {
								int inc = need_space / 3;
								inc = (inc < 256) ? 256 : inc;
								inc = (inc > 8192) ? 8192 : inc;
								new_buffer = new byte[need_space + inc];
							}

							if (unread_size > 0)
								System.arraycopy(buffer, read_pos, new_buffer,
										0, unread_size);

							buffer = new_buffer;

							read_pos = 0;
							write_pos = unread_size;
						}

						System.arraycopy(buff, 0, buffer, write_pos, avail);
						write_pos += avail;

						synchronizer.notifyAll();
					}
				} catch (IOException e) {
					synchronized (synchronizer) {
						exception = e;
						synchronizer.notifyAll();
						break;
					}
				}
			}
		}
	}

	private InputStream is;
	private GobblerThread t;

	private Object synchronizer = new Object();

	private boolean isEOF = false;
	private boolean isClosed = false;
	private IOException exception = null;

	private byte[] buffer = new byte[2048];
	private int read_pos = 0;
	private int write_pos = 0;

	public StreamGobbler(InputStream is) {
		this.is = is;
		t = new GobblerThread();
		t.setDaemon(true);
		t.start();
	}

	@Override
	public int available() throws IOException {
		synchronized (synchronizer) {
			if (isClosed)
				throw new IOException("This StreamGobbler is closed.");

			return write_pos - read_pos;
		}
	}

	@Override
	public void close() throws IOException {
		synchronized (synchronizer) {
			if (isClosed)
				return;
			isClosed = true;
			isEOF = true;
			synchronizer.notifyAll();
			is.close();
		}
	}

	@Override
	public int read() throws IOException {
		synchronized (synchronizer) {
			if (isClosed)
				throw new IOException("This StreamGobbler is closed.");

			while (read_pos == write_pos) {
				if (exception != null)
					throw exception;

				if (isEOF)
					return -1;

				try {
					synchronizer.wait();
				} catch (InterruptedException e) {
				}
			}

			int b = buffer[read_pos++] & 0xff;

			return b;
		}
	}

	@Override
	public int read(byte[] b) throws IOException {
		return read(b, 0, b.length);
	}

	@Override
	public int read(byte[] b, int off, int len) throws IOException {
		if (b == null)
			throw new NullPointerException();

		if ((off < 0) || (len < 0) || ((off + len) > b.length)
				|| ((off + len) < 0) || (off > b.length))
			throw new IndexOutOfBoundsException();

		if (len == 0)
			return 0;

		synchronized (synchronizer) {
			if (isClosed)
				throw new IOException("This StreamGobbler is closed.");

			while (read_pos == write_pos) {
				if (exception != null)
					throw exception;

				if (isEOF)
					return -1;

				try {
					synchronizer.wait();
				} catch (InterruptedException e) {
				}
			}

			int avail = write_pos - read_pos;

			avail = (avail > len) ? len : avail;

			System.arraycopy(buffer, read_pos, b, off, avail);

			read_pos += avail;

			return avail;
		}
	}
}
